1. Field of the Invention
This invention relates to microwave devices. In particular, his invention relates to power amplifiers.
2. Description of Related Art
Radio frequency (RF) high power amplifiers (HPA) are used in any applications such as radio frequency interference (RFI), electromagnetic interference (EMI) testing, lab equipment, communication, television broadcasting, land mobile communications, wireless communication services. These HPA usually have a frequency range between a few hundred MHz to several GHz with output power at several watts to several hundred watts. The desirable features of the HPA include high linearity, wide frequency range, low distortion and low noise figure.
Maintaining linearity of the HPA responses over the operating power range is a difficult problem. Not only the amplitude, or power gain, response needs to be linear, but the phase response should also be linear over the entire power range. Although at low power, the linearity for amplitude and phase can be achieved, as power increases, the amplitude and phase responses tend to be distorted, resulting in nonlinear characteristics.
Accordingly, there is a need in the technology to provide an efficient technique to linearize the amplitude and phase responses for high power amplifiers over the operating power range.